<h2>DESCRIPTION</h2>

<em>v.db.univar</em> calculates basic univariate statistics for numeric
attributes in a vector attribute table. It will calculate minimum, 
maximum, range, mean, standard deviation, variance, coefficient of 
variation, quartiles, median, and 90th percentile. 

<p><em>v.db.univar</em> uses <em>db.univar</em> which in turn uses
<em>db.select</em> to get the attribute values on which it calculates the
statistics.  This means that statistics are calculated based on the entries in
the attribute table, not based on the features in the map. One attribute value
is read from each line in the attribute table, whether there are no, one or
several features with the category value referenced by that line, or whether any
features have more than one category value.  For feature-based, instead of
attribute table-based, univariate statistics on attributes see <a
href="v.univar.html">v.univar</a>.

<em>NOTES</em>

A database connection must be defined for the selected vector layer.

<h2>EXAMPLES</h2>

<h3>Univariate statistics on attribute table column</h3>

In this example, the 30 years precipitation data table is statistically
analysed (North Carolina sample dataset) and univariate statistics performed:

<div class="code"><pre>
# show columns of attribute table connected to precipitation map
v.info -c precip_30ynormals

# univariate statistics on 30 years annual precipitation in NC
v.db.univar precip_30ynormals column=annual
 Number of values: 136
 Minimum: 947.42
 Maximum: 2329.18
 Range: 1381.76
 Mean: 1289.31147058823
 [...]
</pre></div>


<h3>Univariate statistics on randomly sampled data points</h3>

In this example, random points are sampled from the elevation map
(North Carolina sample dataset) and univariate statistics performed:
<div class="code"><pre>
g.region raster=elevation -p
v.random output=samples n=100
v.db.addtable samples column="heights double precision"
v.what.rast samples raster=elevation column=heights
v.db.select samples

v.db.univar samples column=heights
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="db.univar.html">db.univar</a>,
<a href="r.univar.html">r.univar</a>,
<a href="v.univar.html">v.univar</a>,
<a href="db.select.html">db.select</a>,
<a href="d.vect.thematic.html">d.vect.thematic</a>,
<a href="v.random.html">v.random</a>
</em>

<h2>AUTHOR</h2>
 Michael Barton, Arizona State University
<p>and authors of <em>r.univar.sh</em> (Markus Neteler et al.)

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